French historian, b. at Paris, 8 October, 1553; d. there, 7 May, 1617. The son of Christophe de Thou, first president of the Parlement of Paris, he studied at several French universities, especially at Valence, where he knew Scaliger. Both when he accompanied the ambassador Paul de Foix to Italy (1572-76) and when he went to live in Guienne (1581), it was always his aim to make the acquaintance of the most celebrated men of intellect, such as Muretus, P. Manutius, the Pithous, and Montaigne. During his sojourn in Guienne he knew Henry of Navarre, the future Henry IV. As Master of Petitions of the Parlement of Paris in 1585 and in 1588 as councillor of State, he was the opponent of the League. After the assassination of the Duke of Guise he did much to further the reconciliation between Henry III and Henry of Navarre (April, 1589) and set out for Germany with Gaspard de Schomberg to ask the help of Protestant princes against the League. After the death of Henry III he entered the service of Henry of Navarre, with whom he lived for five years in camp. He had an important share in the conferences of Surennes, which prepared the entry of Henry IV into Paris (22 May, 1594) and especially in compiling the Edict of Nantes (1598) which established the religious liberty and political influence of the Protestants. During the regency of Maria de' Medici he took part in the negotiation of the Treaties of Sainte Menehould (1614) and Loudun (1616) between the Court and the rebellious Conde. His influence in the royal councils was exercised in behalf of Gallican ides and he was victorious in his opposition to the reception in France of the Tridentine decrees.

An eminent Latinist, De Thou published several collections of Latin poems, but his fame is chiefly due to his "Historiae" written in Latin. His father, Christophe de Thou (1508-82), having left numerous materials for a national history, De Thou set to work writing it in 1591. His correspondence with foreign scholars procured for him valuable documents. In 1604 he published the first part, 1546-60; in 1606, the second, to 1572; in 1607, the third, 1572-74; and in 1608, the fourth part, 1574-84. He intended carrying it down to the end of the reign of Henry IV (1610), but his narrative had reached only the year 1607, when he died. The last and unfinished portion of his work was published in 1620 by his friends Dupuy and Rigault. The best edition of the Latin text was prepared in the eighteenth century by the Englishman Thomas Carte, published at London in seven volumes by Samuel Buchley (1733); there are French translations and summaries. At first the influence of Cardinal d'Ossat and of Du Perron put off the condemnation of his work at Rome, but in 1609 to De Thou's great sorrow the Congregation of the Index pronounced against it. The Parlement of Paris replied by condemning Cardinal Bellarmine's book on the power of the pope. In his work De Thou commits errors of fact and of appreciation. In his judgment of Mary Stuart, for example, he is too often influenced by Buchanan, an impassioned enemy of the queen's memory. But such as it is his work has a certain value; Bossuet often made use of it in his "Histoire des variations", and he speaks of De Thou as a "great author, a faithful historian".

In 1620 were published his "Memoirs" in Latin: they cover the period between 1553 and 1601 and are an important source for the religious and literary history of the period. Some writers have claimed that his friend, Nicolas Rigault, was their chief author. The eldest son of Jacques-Auguste de Thou, Francois-Auguste de Thou (1607-42), was beheaded at the command of Richelieu for having kept secret the conspiracy between Cinq-Mars and the Spaniards. The library collected by Jacques-Auguste was famous; it was open to scholars and foreigners. In his will De Thou appointed Pierre Dupuy his children's librarian. The library remained in the family until 1680 when it was bought almost entirely by President de Menars and in the eighteenth century passed to the Rohan Soubise family. It then contained 12,729 works. Successive catologues published during the seventeenth century are very important bibliographical documents.